The isolation of substances from plant and animal sources which effect the growth and differentiation of normal and malignant human cells is paramount in the study of the processes which control cellular activities. By studying these materials as biochemical tools, we may be able to understand the biochemical mechanisms controlling cell proliferation and differentiation. Also, by investigating points where control of metabolic pathways are possible, we may find agents to control cellular growth, differentiation and proliferation. Rat liver regenerative stimulator substance and normal hepatic regeneration are affected by a diurnal rhythm. Reversal of controlled lighting reverses these rhythms in normal animals. The phytohemagglutinin isolectins show different interactions with serum components leading to artifactual estimates of their interactions with white or red blood cells. Binding of isolectins to normal erythrocytes shows a constant number of binding sites but alteration of binding constant in the E subunits vary.